[taneq]

I read most of the Dune books back when I was a teenager, and despite being a usually voracious reader I found them very hard to get into. Worth the effort, mind you, but it's definitely a series which requires some investment.

[peckrob]

This is very close to how I feel about Kim Stanley Robinson's Mars trilogy. I read them because many of my friends who were also sci-fi readers raved about them.

I enjoyed Red Mars but I really had to slog through Green Mars and Blue Mars. Red Mars was fun and interesting, but I could have done without a few hundred pages of Sax Russell talking about plants in Green Mars.

I think worldbuilding books take a certain level of investment, even among voracious readers.